Multispeed planetary gear drives are commonly used to drive large earth boring augers. These augers can be used for numerous operations. They are commonly used to dig large cylindrical holes for use in setting utility poles or piers. These same gear drives are used to drill anchors and anchor foundations into the soil.
These gear drives typically have two speeds or gear sets for rotating the auger. The first gear set is used when drilling under normal soil conditions. The second gear set is geared lower. That is to say one rotation of the drive motor output shaft provides more degrees of rotation when using the first gear set than when using the second gear set. Thus if operation of the auger in the first gear set hits soil conditions that stall out the drive motor, the gear drive can be shifted to the second gear set which provides a greater mechanical advantage for the motor.
The prior art gear shift used linkages with various length and alignment adjustments. See FIG. 1. These can be set to optimum conditions during the manufacture. All shifting forces and biasing forces are from the hydraulic cylinder. There are no external springs or biasing means on the gear shift lever itself. As the gear drive is used, these linkages wear leading to misalignment of the prior art gear shift. In extreme cases this can lead to binding and inoperability of the gear shift. These linkages can be adjusted in the field. But aligning these linkages is difficult at best, especially when done by someone who is not trained to perform this task. Further, the individual in the field would likely not have the precision measurement tools necessary to obtain a proper alignment.
What is needed, therefore, is a gear shift mechanism which does not require adjustment to the alignment.